The present invention relates to a continuously variable transmission to be mounted on a vehicle and, specifically, to a technique effectively applied to a continuously variable transmission having a rubber drive belt.
A belt-driven continuously variable transmission (CVT) applied to a power transmission system of the vehicle has a primary pulley provided on an input shaft and a secondary pulley provided on an output shaft, wherein the drive belt is provided to extend for winding between the two pulleys. By changing the contact diameter of the drive belt, a rotation speed transmitted from the input shaft to the output shaft is changed continuously.
In such a continuously variable transmission, the contact diameter of the drive belt is changed. Therefore, there are a hydraulic type one in which a groove width of the primary pulley is variably controlled by hydraulic pressure in accordance with a run condition, and a weight type one in which a groove width of the primary pulley is variably controlled by centrifugal weight in accordance with the rotation speed of the primary pulley.
The hydraulic-type continuously variable transmission is more suitable than the weight-type one to high-precisely control a transmission gear ratio depending on the run condition. However, the hydraulic-type continuously variable transmission requires a hydraulic control device, which performs hydraulic control in accordance with the run condition of the vehicle, so that adoption of the hydraulic-type continuously variable transmission involves cost increase. In contrast, the weight-type continuously variable transmission is capable of being changed in accordance with the rotation speed of the primary pulley, so that its construction is simple and, consequently, the manufacturing costs of the continuously variable transmission can be reduced. For these reasons, the weight-type continuously variable transmission is mounted on all terrain vehicles (ATVs) and two-wheel vehicles, etc. in many cases.
A rubber drive belt is built in the weight-type continuously variable transmission, and the drive belt requires being cooled for preventing its deterioration and improving its durability. Therefore, there has been developed a continuously variable transmission in which, by providing fan blades on the primary pulley, cooling air is blown into a case in which the pulley and drive belt are accommodated (see, for example, Japanese Patent Laid-open (TOKUKAIHEI) 11-11171).